Gas mixing devices are generally divided into three categories: mass flow controlled blending devices, partial pressure mixing devices, and mass weight control mixing devices.
Current gas mass flow controlled mixing devices for mixing oxygen with air or nitrogen, are expensive and require precise knowledge and control of the two gasses before being mixed together. Any variation from the known concentrations of the gasses prevents an accurate mixing of the gasses to a desired oxygen concentration.
Partial pressure gas mixing devices require extensive operator interface and, as with gas mass flow controlled devices also require extensive knowledge and control of the exact oxygen concentrations before mixing of the gasses. Furthermore, these devices suffer from latent inaccuracies in mixing of the gasses.
Devices which mix gasses by means of mass weighing also require precise knowledge of the two gasses being mixed and expensive weighing and control devices.
As indicated above, each of the above discussed prior art devices requires accurate knowledge of the input gasses and expensive analysis and display of oxygen content after mixing to ensure accuracy. These devices are also often susceptible to pressure and temperature sensitivity.